In addition to an electronic brake system (EBS), utility vehicles also have, for safety reasons, a pneumatic brake system which makes available a redundant function and is used if, for example, the electronic brake system fails. For this purpose, what are referred to as backup valves are arranged on wheel modules of a utility vehicle, which backup valves are energized in the fault-free normal operating mode with the control pressure which is requested by the driver of the utility vehicle, from the compressed air system of the utility vehicle, but said backup valves themselves remain closed. In the event of failure of the electronic brake system, the backup valve is opened and said backup valve applies the brake pressure which is present at it, while the normal inlet and outlet valves are closed.
Such backup valves are generally embodied as solenoid valves which are known per se, and may be used in vehicles, for example utility vehicles, for converting electrical control pulses into, inter alia, hydraulic or pneumatic control pulses for controlling, for example, automatically or electronically controlled transmissions or electronic brake systems.
In this context, rear axle modules in electronic brake systems by which two backup valves are actuated by a control unit by pulse width modulation are known.
If a plurality of valves are present, usually one on each wheel module of the utility vehicle, a plurality of actuation devices have hitherto been used depending on the number of backup valves, for example in each case a separate valve output stage has been used for each backup valve to be actuated, in order to actuate said backup valves independently.
This disadvantageously results in increased expenditure on components as well as more complex actuation, entailing, in particular in the vehicle sector, undesirably high costs and greater expenditure on development. In addition, a larger number of components in the entire system results in a higher risk of failure and therefore can make the vehicle less economically viable.
Furthermore, document U.S. Pat. No. 5,752,482 discusses a load driver system for integrally controlling a current flow through a number of inductive loads of an internal combustion engine such as an injection nozzle coil and a motor brake coil during operation of a motor cylinder, document DE 196 32 365 C1 discusses a circuit arrangement for switching a plurality of parallel inductors independently of one another, document EP-A-1 422 815 discusses a method and a device for actuating an electrical load, in which an energy accumulator takes up the energy of an inductive element when a switch opens, document DE 42 05 563 A1 discloses a solenoid coil for valves with a secondary coil parallel to a temperature-dependent resistor, and document DE 10 2004 007209 B4 discusses a circuit arrangement and a method for determining the load current through an inductive load which is applied to a supply voltage in a clocked fashion.